Abstract: The dynamic air bearing force and asperity contact force of precision H-type air bearings are calculated considering the effect of air rarefaction and surface roughness. The axial motion of the rotor and the minimum air film thickness is obtained. The effect of both the number and depth of spiral grooves on the startup behaviors of the air bearing is discussed. The results show that the air bearing force increases with an increase in the angular velocity of the rotor. When the angular velocity is about 200 r/min, the rotor fully separates with the air bearing surface. The increasing spiral groove number leads to an increase in the air bearing force and a decreased in the contact force. However, slight change in the air bearing force and contact force is generated when the groove number is over 10. Considering the cost and efficiency for manufacturing the spiral grooves, the optimal groove number of the air bearing is 10. With an increase in the groove depth, the air bearing force first increases and then decreases, while the asperity contact force first decreases and then increases. When the groove depth is 1.5 μm, a maximum air bearing force and a minimum asperity contact force are generated. Therefore, under the startup condition of the air bearing, the optimal groove depth is 1.5 μm.

Key words: air rarefaction, asperity contact, precision H-type air bearing, startup process